Burring is a machining technique involving punching a hole in a workpiece such as a metal sheet to form a flange (or a boss) along the edge of the hole. A burring apparatus typically includes a burring punch and a burring die, inside of which a burring hole is formed. A workpiece is placed on the top stage of the die, and a tip of the burring punch is pressed onto the workpiece above the burring hole so as to make a hole with a boss in the workpiece by punching off the corresponding metal piece. These punched-off metal pieces are scraps that need to be discarded properly. In a conventional burring process, however, it is often the case that these scraps get magnetized and attached to the tip of the burring punch, thereby interfering with the subsequent punching operation, or attached to the newly formed boss, thereby requiring cleaning of the product.